The present invention pertains to surface-modified colloidal abrasive (e.g., ceria) polishing compositions (and associated methods using these compositions) wherein the modified colloidal abrasives are negatively-charged colloids (with the exception of modified colloidal titania, which is a positively-charged colloid), which remain negatively-charged in acidic media, and which are gel-free. These compositions are especially useful for chemical mechanical planarization (chemical mechanical polishing, CMP).
Certain modifications of colloidal abrasive compositions are known. Colloidal silica, for example, has been modified with various metallic compounds as disclosed in U.S. Pat. Nos. 3,252,917, 3,745,126, and 3,620,978; EP Patent Publication 1 000 995 A1; and also in the book entitled xe2x80x9cThe Chemistry of Silicaxe2x80x9d, R. K. Iler, Wiley Interscience (1979), pages 410-411. Colloidal silica has been stabilized with boric acid as disclosed in U.S. Pat. No. 2,630,410.
The invention in one embodiment is a composition for chemical-mechanical planarization comprising:
a) a boron surface-modified colloidal abrasive containing a boron compound on the surface of the abrasive, wherein the boron compound is present on the surface of the abrasive at a level of at least 20 percent of available surface sites; and
b) an acid.
The invention in another embodiment is a composition for chemical-mechanical planarization comprising:
a) a boron surface-modified colloidal abrasive containing a boron compound on the surface of the abrasive, wherein the abrasive is selected from the group consisting of colloidal ceria and colloidal titania; and
b) an acid.
The invention in still another embodiment is a method of chemical-mechanical planarization comprising the steps of:
A) placing a substrate in contact with a polishing pad;
B) delivering a composition comprising:
a) a boron surface-modified colloidal abrasive containing a boron compound on the surface of the abrasive, wherein the boron compound is present on the surface of the abrasive at a level of at least 20 percent of available surface sites; and
b) an acid; and
C) at least partially planarizing the substrate with the composition.
The invention in still another embodiment is a method of chemical-mechanical planarization comprising the steps of:
A) placing a substrate in contact with a polishing pad;
B) delivering a composition comprising:
a) a boron surface-modified colloidal abrasive containing a boron compound on the surface of the abrasive, wherein the abrasive is selected from the group consisting of colloidal ceria and colloidal titania; and
b) an acid; and
C) at least partially planarizing the substrate with the composition.
The CMP methods of this invention are especially useful in planarizing various substrates utilized in semiconductor manufacture.
While certain metal modifications of various colloidal abrasives are known as disclosed in the aforementioned references, none of these references though discloses that boron surface-modified colloidal abrasives, such as boron surface-modified colloidal silica, being negatively charged and maintaining their charges even in acidic media as well as the gel-free and floc-free advantages of these boron surface-modified colloidal abrasives. In addition to the floc-free properties, boron surface-modified colloidal silica is stable under acidic as well as basic conditions over a broad pH range from pH=1.5 to pH=9.
This invention entails gel-free surface-modified colloidal abrasive polishing compositions and associated processes utilizing these modified abrasive polishing compositions. The gel-free abrasive compositions of this invention are useful not only for polishing base materials (e.g., bare silicon wafers) but also these compositions are especially useful for chemical mechanical planarization (CMP, chemical mechanical polishing) of layers in fabricating semiconductor chips/devices. CMP is now widely known to those skilled in the art and has been described in numerous patents and open literature publications. Some introductory references on CMP are as follows: xe2x80x9cPolishing Surfaces for Integrated Circuitsxe2x80x9d, by B. L. Mueller and J. S. Steckenrider, Chemtech, February, 1998, pages 38-46; and H. Landis et al., Thin Solids Films, 220 (1992), page,1. A preferred use of the modified abrasive polishing compositions of this invention is for CMP.
The modified abrasive polishing compositions of this invention comprise a boron surface-modified colloidal abrasive particle. Gel-free colloidal abrasives useful as components in the polishing compositions of this invention include, but are not limited to, colloidal silica, colloidal ceria, and colloidal titania.
A boron surface-modified colloidal abrasive particle is obtained by treatment of a colloidal abrasive particle with a boron-containing compound as detailed infra. Suitable boron-containing compounds to effect boron surface-modification include, but are not limited to, boric acid, boron trichloride, boron trifluoride, and trialkoxy borane. Boric acid is preferred.
A given boron surface-modified colloidal abrasive particle in a composition of this invention has at least 20% of sites on the surface of the colloidal abrasive particle covered by the boron-containing compound and/or other boron-containing compound(s) derived from the boron-containing compound. Preferably, a given boron surface-modified colloidal abrasive particle in a composition of this invention has from about 40% to about 95% of surface sites of the colloidal abrasive particle at least covered by the boron-containing compound and/or other boron-containing compound(s) derived from the boron-containing compound. More preferably, this range of surface coverage on the surface-modified colloidal abrasive particle is from about 80% to about 95%. The percentage of surface sites covered on a colloidal abrasive particle in a composition of this invention can range up to 100%.
Some embodiments of this invention are compositions for chemical-mechanical planarization that comprise a) a colloidal abrasive whose surface has been modified to contain a boron-containing compound and/or other boron-containing compound(s) derived from the boron-containing compound and b) an acid. Suitable boron surface-modified colloidal abrasives include, but are not limited to, boron surface-modified colloidal silica, boron surface-modified colloidal ceria, and boron surface-modified colloidal titania. Boron-modified colloidal silica is preferred in the CMP method embodiments of this invention. Other details (e.g., suitable boron-containing compound(s) and percentage of sites on the colloidal abrasive particle by the boron-containing compound(s)) are as given supra.
Suitable acid components for these compositions include, but are not limited to, sulfuric acid, hydrochloric acid, nitric acid, hydrofluoric acid, phosphoric acid, periodic acid, and organic acid(s). Inorganic acids are preferred. For use in metal chemical mechanical planarization (CMP) applications, oxidizing acids (e.g., periodic acid) are preferred. The compositions of this invention can contain one or more acids, which in the latter case, independently can be either oxidizing acids or non-oxidizing acids.
The compositions of this invention can further comprise an oxidizing agent. Suitable oxidizing agents include, but are not limited to, periodic acid, hydrogen peroxide, and sodium iodate. Periodic acid is a preferred oxidizing agent especially when the acid component is chosen to be a non-oxidizing acid (e.g., sulfuric acid).
The amount of surface-modification of the colloidal abrasive with a boron-containing compound(s) according to this invention in order to insure a gel-free composition depends upon the average size of the colloidal abrasive particles. Colloidal abrasive particles that are smaller and which consequently have less surface area generally require higher levels of surface modification than do larger particles, which have more surface area. As an illustrative example for boric acid surface-modified colloidal silica, the various sizes of colloidal particles required the approximate levels of boric acid modification as shown below in order to achieve good stability towards gel formation in acidic media, such as metal CMP polishing compositions.
Analytical method for measuring the surface coverage of surface modified silica The amount of surface coverage of boric acid on the silica surface was measured using a Colloidal Dynamics instrument, manufactured by Colloidal Dynamics Corporation, 11-Knight Street, Building E8, Warwick, R.I., 02886. The Colloidal Dynamics instrument measures the zeta potential (surface charge) of the surface modified silica particles. During the preparation of boric acid modified silica, boric acid is added to the de-ionized silica particles, the addition of boric acid changes the zeta potential of the silica particle surface. After reaching the full surface coverage, there is no change in the zeta potential of the surface modified silica. From this titration curve of zeta potential as a function of gram of boric acid to a given amount of silica, we measured % surface coverage of boric acid on the silica surface.